Method of forging sintered articles of high density

ABSTRACT

A method of forging sintered articles of high density characterized in that pre-shaped powdery articles are heated to a temperature of 1120*-1200*C and then are forged by a tool, which is pre-warmed to 80*-120*C and maintained at such pre-warming temperature, at a tool speed of 7-10m/second. The articles thus forged are rapidly separated from the tool through the medium of an ejector provided on the forging machine.

United States Patent Gate Mar. 5, 1974 [54] METHOD OF FORGING SINTERED2,821,016 H1958 Dickson 72/342 ARTICLES OF H DENSITY 3,645,728 2/1972Hrinevich, Jr. 29/4205 3,605,245 9 1971 Zapf 29 4205 [76] Inventor:Saburo Goto, 49-Banchl, Shrchrku Kamiumenoki-cho, Kita-ku, Kyoto, JapanPrimary ExamznerL0well A. Larson Attorney, Agent, or FirmWenderoth, Lind& Ponack [22] Filed: Jan. 21, 1972 l [2 1 App] No 219,652 ABSTRACT [30]Foreign Application Pri i Data A method of forging sintered articles ofhigh density Oct 7 I971 Ja an M8909 characterized in that pre-shapedpowdery articles are p heated to a temperature of ll20l200C and then areforged by a tool, which is pre-warmed to 8|. 72/342,B and maintained atSuch pre warming term I peramre, at a too] speed of 7 10m/second Thearti [58] Field of ch 29/4205 72/342 cles thus forged are rapidlyseparated from the tool [56] References Cited through the medium of anejector provided on the forging machine.

UNITED STATES PATENTS 8/1956 Boegehold et al. 29/4205 3 Claims, 1Drawing Figure METHOD OF FORGING SINTERED ARTICLES OF HIGH DENSITYBACKGROUND OF THE INVENTION This invention relates to a method offorging whereby the necessity of the precise forged articles of highdensity can be produced without re-sintering process of moulding.

This invention is characterized in that powdery articles, pre-shaped bya conventional method or by a specific method, are heated to atemperature of ll20 1200C, while a tool is pre-warmed to a temperatureof from 80 to 120C and is maintained at this prewarming temperature. Theheated articles then are forged in the tool at a speed of 7 lm/second.forging, the finished forged article and the tool are separated rapidlyby a separating apparatus provided on the forging machine.

High density is essential for sintered articles such as forged machineparts. In this respect, US. Pat. No. 3,410,683 discloses the methodwhereby a molded article is heated to a temperature of about 750C 1 100Cbefore it is re-pressed, and the press tool is pre-warmed to atemperature of 150C 350C and is maintained at this pre-warmingtemperature throughout the repressing operation, in order to keep therecrystallisation conditions of the article during re-processingconstant. It appears that the purpose of this method is to obtainprecise finished articles by maintaining the temperature of the presstool high and by maintaining the temperature of article low or from 750Cto 1 100C so as to reduce the temperature difference between the tooland the material, thereby avoiding temperature drop of the article asfar as possible and thus increasing the fluidity of the material.However, the lower temperature of the actually material results inlowering the fluidity and consequently lowering the degree ofpreciseness of the finished article. Moreover, since the press tool isbulky, it is extremely difficult to maintain its temperature high.

The most important problem raised in hot forging is that during theprocessing of a highly heated article on the press tool, the surfacetemperature of the tool rises and the surface of tool is transformed dueto thermal fatigue and wear. A finished article, after separation fromthe tool, is cooled by compulsory cooling but it is difficult to preventthe rising of its temperature due to conduction of heat at the contactsurface with the tool during processing. Thus, the best way for forginga powdery substance is to process the heated substance as quickly aspossible. Furthermore, a faster tool speed and a shorter processing timeimprove the flow of the material of a preshaped sintered article,decrease the coefficient of kinetic friction and effect the uniformdistribution of pressing force into every part of the finished article,with the result of uniform density. The forging machine primarily usedis an oil-pressure forging press of low processing speed (0.6m/second orlower). Presses such as the drop hammer, friction press, etc., work atthe medium speed or 2 4m/second, and a forging machine of the upwardpressurizing type works at the high speed of 7 lOm/second.

As is obvious from the foregoing, the time during which the tool makescontact with a heated article decreases in inverse proportion to thetool speed. Therefore, when using a forging machine of low speed, the

temperature of the tool must be kept at least as high as 350C, orotherwise the article undergoes a large temperature drop at the area incontact with the tool, with the result of uneven density due to thepartial difference in cooling speed. On the other hand, when a forgingmachine with a high processing speed, such as DYNAPACK, is used, thewear of the tool is large due to the longer time required forseparation, even though the operating speed is high (12 l9m/second).

SUMMARY OF THE INVENTION In the present invention, a forging machinehaving a high processing speed and a shorter tool separation time isused, for example, a forging machine of the KJ H series. This type offorging machine belongs to the group of hammering machines of the upwardpressurizing type. It works at a speed of 7 lOm/second and is equippedwith a tool separating apparatus such as an ejector. It provides optimumconditions for obtaining the uniformly high density of the powderyarticle during forging because of the synchronization of the dropping ofan upper tool and the rising of a lower tool. In the present invention,a lubricant may be applied to the tool, instead of adding a lubricant tothe powdery substance.

BRIEF DESCRIPTION OF THE DRAWINGS The single FIGURE is a microscopicphotograph of a finished article forged in accordance with the presentinvention.

EXAMPLE OF INVENTION The result of test forging carried out by using theabove discussed forging machine in accordance with the temperature andother limitations of the process of this invention was as follows:

Forging conditions:

Pre-shaped powder: Electrolytic iron powder Pressed powder density:6.8g/cm Forging temperature: 1 180C Heating duration: 30 minutes(hydrogen atmosphere) Processing energy: 0.7 ton m Tensile CharpyDensity strength Elongation impact value g/cc kg/mm Kgm/cm 7.85 26.2455.7 30 or more As is obvious from the above test results, forgedarticles produced according to the present invention exhibit superiorphysical properties to conventionally forged articles.

What is claimed is:

l. A method for forging a sintered article having a high density, saidmethod comprising:

pre-heating to a temperature of 80-120C the forging tool of a forgingmachine of the type having an upper element and a lower element movabletogether in syncronization;

heating a pre-shaped powdery article to a temperature of ll20l200C;

forging said heated pre-shaped powdery article by said pre-heated toolat a forging operating speed of ing is accomplished by a synchronizedlowering of said upper element and raising of said lower element.

3. A method as claimed in claim 1, wherein said preshaped powderyarticle is heated to a temperature of 1 -l200C.

2. A method as claimed in claim 1, wherein said forging is accomplishedby a synchronized lowering of said upper element and raising of saidlower element.
 3. A method as claimed in claim 1, wherein said preshapedpowdery article is heated to a temperature of 1180*-1200*C.